Science fiction movies and novels are awesome to read and to fantasize about but they often gloss over the many downsides of deep space travel. In this post I am going to go over just a few of those.

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##### Breathing in your colleague's farts You will be stuck in a tin can that has a fairly small and finite volume. The International Space Station ([ISS](https://en.wikipedia.org/wiki/International_Space_Station)) for instance has a habitable volume of just 930 cubic metres. The typical human produces 500 mL to 1500 mL of flatulence [per day](https://en.wikipedia.org/wiki/Flatulence). That's one-half to one-and-a-half litres per day. If a deep space mission craft has the same volume as the ISS and there are, say 10 crew members, on board that's a total daily flatulence volume of up to 15 litres per day or about 1.6% of the ship's cabin volume. Let's hope the craft's air scrubber is super-efficient. On the bright side this is probably no worse than your average office environment.

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##### Dust It is said that household dust is composed of human hair, human skin cells, animal hair, plant pollen, textile fibers, dust from outside minerals, dust mites and dust mite feces. On a space craft plant pollen, mineral dust and animal hair will likely be absent. The rest you will be breathing in all day, every day. Once again, let's hope the air filtration system is super-efficient. ##### Cabin Fever If you live in the North no doubt you are familiar with the term "cabin fever". Maybe your country has a different word for it but that is what we call it here in Canada. At the end of a long, cold winter after having huddled up in our houses for 6 months we are all basically climbing the walls. Then springtime comes and we all burst out into the sun like groundhogs emerging from their dens after a long winter's hibernation.

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Fast forward to a long Mars mission. It will take 4 to 6 months to get there and when you land you will be living in a tin can on the surface with only the occasional expedition outside. If you are feeling cooped up and just need to go for a walk to take some time off to just be by yourself, well you are out of luck. The procedure for getting out of your landing craft will no doubt be slow and arduous and only used for specific and purposeful activities. No more just going for a walk-about to clear your head. The psychological stresses of a deep space mission will likely be one of the biggest challenges that the space explorers will have to face. ##### Radiation If farts, dust and cabin fever were not bad enough there is also the ever present hazard due to radiation. Radiation will come from two main sources: the solar wind and cosmic rays. Neither of these will be good for your health or your gonads. It is likely that the walls of the astronauts' living quarters will be surrounded by water tanks that will act as radiation shields. However there will be mass considerations for the space craft and it is likely that the shielding will not block all of the radiation entering the crew cabin. The crew will no doubt have to simply accept the risk of radiation damage to their DNA and the increased likelihood of cancer as well as immune system damage.

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##### Going to the Bathroom Did you ever wonder why space movies never show people going to the bathroom? Well the reason is that pooping in zero g sucks. Literally. The bathroom facility on the ISS is basically a vacuum pump that, ahem, sucks the liquid and solid waste away from the astronauts. If the system ever malfunctions or you just screw up and make a mess well you are going to have a bad day. Getting sick and barfing will also be no picnic especially if you miss your barf bag. ##### Recycled Urine To maintain a healthy fluid balance a typical human will need 3 to 4 litres of water per day. For a 10 person crew that will be 30 to 40 litres per day on average. What goes in must come out, ..., in the form of urine.

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This basically means that the ship will need to collect and recycle the urine, processing it and producing new drinking water for the next day's consumption. Yummy. Having said that we here on Earth also are drinking water that someone, or some animal has at one time or another urinated out onto the ground. However the causal connection here on Earth is hopefully a little more distant than the short loop that would exist on a space ship. On a space ship, you will know who's urine you are drinking. Being philosophical this also means that one of you may have consumed at least one molecule of Aristotle's urine today. Do you feel any smarter for the experience? ##### Bone Loss It is now a well documented fact that living in zero g also contributes to significant [bone material loss](https://www.dartmouth.edu/~humbio01/s_papers/2002/Bruce.pdf). This is an area of ongoing space health research and astronauts are required to exercise daily to mitigate the effects of this phenomenon. The load bearing bones (ankles, femur, tibia, pelvis and lumbar vertebrae seem to be the most affected. Bone loss rates can be up to 1% to 2% per month meaning a possible 12% bone mass loss on a trip to Mars. The gravity on Mars is about 40% that of Earth and hopefully this will be sufficient to halt and maybe even reveres the degradation?

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##### Changes in Genetic Expression Astronaut Scott Kelly spent a year in space. Fortuitously for science he also has a twin brother who stayed on Earth. This provided a great opportunity for a controlled experiment in which to study the effects of a zero-g environment on the [expression of a human's genes](https://www.youtube.com/watch?v=NpdwOdi3Xt0). It was found that his year long space trip significantly altered the expression of his genes and that after some time back on Earth about 7% of that change in genetic expression has [stayed the same](https://www.livescience.com/62000-scott-kelly-dna-twin-study.html), implying that it may be permanent. It is not said whether these changes are beneficial, detrimental or just benign but it will be a factor to consider for deep space travelers of the future.

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##### Death is only Millimetres Away As mentioned earlier, the mass of the space craft will be a very important consideration. This means: the lighter the better. This also means that the walls of the craft will only be millimetres thick. The astronauts will be traveling something like 10 to 11 kilometres per second in a can with walls that are only a few millimetres thick. Any tiny space pebble is likely to cause a puncture and the astronauts will need to be able to react promptly to fix any resultant holes. Anything larger than a pebble will surely wreak havoc and the psychological stresses of this potential catastrophe will no doubt weigh heavily on the minds of the crew. One would hope that the craft has a very good radar system and will be able to detect and evade anything larger than a grain of sand. ##### No STDs There is one potential benefit to space travel. Everyone on board will be screened and STD-free. Any crew that goes to the Red Planet, or beyond, will very likely be a co-ed affair and for the sake of psychological stability you would expect them to choose mating pairs (or whatever arrangement develops thereafter). However the uncertainties for pregnancy and the impact of a zero-g environment on a developing fetus means that everybody will need to get their tubes tied before departing. On the other hand, the impact of a relationship going bad on a very small ship could be quite bad for crew morale. #### Closing Words Traveling to Mars and beyond will be a great adventure and the first people who go will be remembered forever. This will be incentive enough for them to put up with the minor inconveniences of living in cramped quarters with other people for years as well as the major inconveniences of radiation and other potential space hazards. *Thank you for reading my post.* #### Post Sources [1] [International Space Station](https://en.wikipedia.org/wiki/International_Space_Station) [2] [Flatulence.](https://en.wikipedia.org/wiki/Flatulence) [3] [Household dust.](https://en.wikipedia.org/wiki/Dust) [4] [Drinking water requirments.](https://en.wikipedia.org/wiki/Drinking_water) [5] [Genetic expression in space (pdf).](https://www.dartmouth.edu/~humbio01/s_papers/2002/Bruce.pdf) [6] [Genetic expression in space (youtube).](https://www.youtube.com/watch?v=NpdwOdi3Xt0) [7] [Genetic expression in space -DNA twin study.](https://www.livescience.com/62000-scott-kelly-dna-twin-study.html) [8] [Mars.](https://en.wikipedia.org/wiki/Mars)

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